Adaptively configured and autoranging voltage transformation module arrays

ABSTRACT

A method and apparatus for adaptively configuring an array of voltage transformation modules is disclosed. The aggregate voltage transformation ratio of the adaptive array is adjusted to digitally regulate the output voltage for a wide range of input voltages. An integrated adaptive array having a plurality of input cells, a plurality of output cells, or a plurality of both is also disclosed. The input and output cells may be adaptively configured to provide an adjustable transformer turns ratio for the adaptive array or in the case of an integrated VTM, an adjustable voltage transformation ratio for the integrated VTM. A controller is used to configure the cells and provide digital regulation of the output. A converter having input cells configured as a complementary pair, which are switched out of phase, reduces common mode current and noise. Series connected input cells are used for reducing primary switch voltage ratings in a converter and enabling increased operating frequency or efficiency. An off-line auto-ranging power supply topology is disclosed. An auto-ranging converter module (“ACM”) includes 2 or more input cells magnetically coupled to an output cell providing auto-ranging, isolation, and voltage transformation. The ACM converts a rectified line voltage to a low DC bus voltage. The topology allows regulation and power factor correction to be provided at a low voltage increasing energy density and efficiency and reducing cost.

This application is a continuation-in-part of pending U.S. applicationSer. No. 10/785,465, filed Feb. 24, 2004 the contents of which areincorporated by reference.

TECHNICAL FIELD

This invention relates to the field of electrical power conversion andmore particularly to regulated power conversion systems and off-lineauto-ranging power supplies.

BACKGROUND

DC—DC converters transfer power from a DC electrical input source to aload by transferring energy between windings of an isolationtransformer. The DC output voltage delivered to the load is controlledby adjusting the timing of internal power switching elements (e.g., bycontrolling the converter switching frequency and/or the switch dutycycle and/or the phase of switches). As defined herein, the functions ofa “DC—DC converter” comprise: a) isolation between the input source andthe load; b) conversion of an input voltage to an output voltage; and c)regulation of the output voltage. DC—DC converters may be viewed as asubset of a broad class of switching power converters, referred to as“switching regulators,” which convert power from an input source to aload by processing energy through intermediate storage in reactiveelements. As defined herein, the functions of a “Switching Regulator”comprise: a) conversion of an input voltage to an output voltage, and b)regulation of the output voltage. If the required output voltage isessentially a positive or negative integer (or rational) multiple of theinput voltage, the conversion function may also be efficiently performedby a capacitive “Charge Pump,” which transfers energy by adding andsubtracting charge from capacitors.

Vinciarelli et al, “Efficient Power Conversion” U.S. Pat. No. 5,786,992disclose expanding the operating voltage range of isolated DC—DCconverters by connecting their inputs and/or outputs in series.

Non-resonant full-bridge, half-bridge, and push-pull DC-to-DCtransformer topologies are known. See e.g., Severns and Bloom, “ModernDC-to-DC Switchmode Power Conversion Circuits,” ISBN 0-442-21396-4, pp.78–111. Series, parallel, and other resonant forms of switching powerconverters are also known. See e.g., Steigerwald, “A Comparison ofHalf-Bridge Resonant Converter Topologies,” IEEE Transactions on PowerElectronics, Vol. 2, No. 2, April, 1988. Variable frequency, seriesresonant, half-bridge converters for operation from an input voltagesource are described in Baker, “High Frequency Power Conversion WithFET-Controlled Resonant Charge Transfer,” PCI Proceedings, April 1983,and in Nerone, U.S. Pat. No. 4,648,017. Half-bridge, single-stage, ZVS,multi-resonant, variable frequency converters, which operate from aninput voltage source are shown in Tabisz et al, U.S. Pat. No. 4,841,220and Tabisz et al, U.S. Pat. No. 4,860,184. A variable frequency,full-bridge, resonant converter, in which an inductor is interposedbetween the input source and the resonant converter is described inDivan, “Design Considerations for Very High Frequency Resonant ModeDC/DC Converters,” IEEE Transactions on Power Electronics, Vol. PE-2,No. 1, January, 1987. A variable frequency, ZVS, half-bridge LLC seriesresonant converter is described in Bo Yang et al, “LLC ResonantConverter for Front End DC—DC Conversion,” CPES Seminar 2001,Blacksburg, Va., April 2001. Analysis and simulation of a “Low Q”half-bridge series resonant converter, wherein the term “Low Q” refersto operation at light load, is described in Bo Yang et al, “Low QCharacteristic of Series Resonant Converter and Its Application,” CPESSeminar 2001, Blacksburg, Va., April 2001.

Fixed-frequency half-bridge and full-bridge resonant converters are alsoknown in which output voltage control is achieved by controlling therelative timing of switches. A half-bridge, single-stage, ZVS,multi-resonant, fixed-frequency converter that operates from an inputvoltage source is shown in Jovanovic et al, U.S. Pat. No. 4,931,716. Afull-bridge, single-stage, ZVS, resonant, fixed-frequency converter thatoperates from an input voltage source is shown in Henze et al, U.S. Pat.No. 4,855,888.

A full-bridge, single-stage, ZCS, series-resonant, fixed-frequencyconverter, operating at a frequency equal to the characteristic resonantfrequency of the converter, is shown in Palz, “Stromversorgung vonSatelliten—Wanderfeldröhren hoher Leistung” (“Power Supply forSatellites—High Capacity Traveling-Wave Tubes”), Siemens Zeitschrift,Vol. 48, 1974, pp. 840–846. Half and full-bridge, single-stage, ZVS,resonant, converters, for powering fluorescent tubes are shown inNalbant, U.S. Pat. No. 5,615,093.

A DC-to-DC Transformer offered for sale by SynQor, Hudson, Mass., USA,called a “BusQor™ Bus Converter,” that converts a regulated 48 VDC inputto a 12 VDC output at a power level of 240 Watts and that can beparalleled with other similar converters for increased output powerdelivery, and that is packaged in a quarter brick format, is describedin data sheet “Preliminary Tech Spec, Narrow Input, Isolated DC/DC BusConverter,” SynQor Document No. 005-2BQ512J, Rev. 7, August, 2002.

The art of resonant power conversion, including operation below or aboveresonant frequency, utilizing either ZCS or ZVS control techniques andallowing the resonant cycle to be either completed or purposelyinterrupted, is summarized in Chapter 19 of Erickson and Maksimovic,“Fundamentals of Power Electronics,” 2nd Edition, Kluwer AcademicPublishers, 2001.

Cascaded converters, in which a first converter is controlled togenerate a voltage or current, which serves as the source of input powerfor a DC-to-DC transformer stage, are known. A discussion of canonicalforms of cascaded converters is given in Severns and Bloom, ibid, at,e.g., pp. 114–117, 136–139. Baker, ibid, discusses the use of a voltagepre-regulator cascaded with a half-bridge, resonant, variable-frequencyconverter. Jones, U.S. Pat. No. 4,533,986 shows a continuous-mode PWMboost converter cascaded with both PWM converters and FM resonanthalf-bridge converters for improving holdup time and improving the powerfactor presented to an AC input source. A zero-voltage transition,current-fed, full-bridge PWM converter, comprising a PWM boost converterdelivering a controlled current to a PWM, full-bridge converter, isshown in Hua et al, “Novel Zero-Voltage Transition PWM Converters,” IEEETransactions on Power Electronics, Vol. 9, No. 2, March, 1994, p. 605.Stuart, U.S. Pat. No. 4,853,832, shows a full-bridge series-resonantconverter cascaded with a series-resonant DC-to-DC transformer stage forproviding AC bus power to distributed rectified loads. A half-bridge PWMDC-to-DC transformer stage for use in providing input power topoint-of-load DC—DC converters in a DPA is described in Mweene et al, “AHigh-Efficiency 1.5 kW, 390-50V Half-Bridge Converter Operated at 100%Duty Ratio,” APEC '92 Conference Proceedings, 1992, pp. 723–730.Schlecht, U.S. Pat. Nos. 5,999,417 and 6,222,742 shows DC—DC converterswhich incorporate a DC-to-DC transformer stage cascaded with a switchingregulator. Vinciarelli, “Buck-Boost DC—DC Switching Power Conversion,”U.S. patent application Ser. No. 10/214,859, filed Aug. 8, 2002,assigned to the same assignee as this application and incorporated byreference, discloses a new, high efficiency, ZVS buck-boost convertertopology and shows a front-end converter comprising the disclosedtopology cascaded with a DC—DC converter and a DC-to-DC transformer.

In one aspect, prior art approaches to off-line power conversion may becharacterized by how they accommodate a broad range of nominal linevoltages, e.g., 110 VAC (i.e. 85–120 VAC) and 220 AC (i.e. 170–240 VAC).In one approach, the line is simply rectified and power conversioncircuitry is designed to operate over the full range of variation of therectified line voltage; in another approach, called “auto-ranging”, therectification circuitry is reconfigured based upon the nominal value ofthe line voltage and the range of voltages over which power conversioncircuitry must operate is reduced. In another aspect, off-line powerconversion may be characterized in terms of whether or not power factorcorrection (“PFC”) is provided. Auto ranging is commonly provided innon-PFC power supplies using a capacitive voltage doubler. Referring toFIG. 10 for example, an off-line power supply includes a bridgerectifier 501, capacitors 502 and 503 connected in series across therectifier output, and a doubler switch 506 which may be manually orautomatically controlled for effecting voltage doubling. For high linevoltages e.g. 220 VAC the switch remains open and the rectified voltageV₂ will approximately equal the peak input voltage V_(IN). For low lineapplications, the switch 506 is closed and V₂ will approximately equaltwice the peak input voltage V_(IN) and the voltage V₂ will remainnominally at 220V regardless of whether a 110 or 220 VAC line isconnected at the input. The DC—DC converter 504 provides the voltagetransformation, isolation and regulation functions for power deliveredto the load 505.

Because it requires the use of energy storage capacitors at the outputof the rectifiers, the capacitive voltage-doubler is not generallysuitable for use in PFC applications. Vinciarelli et al., “PassiveControl of Harmonic Current Drawn From an AC Input by RectificationCircuitry,” U.S. Pat. No.6,608,770, issued Aug. 19, 2003, assigned tothe same assignee as this application and incorporated by reference,discloses capacitive voltage-doubling auto-ranging circuitry whichpassively controls the harmonic current drawn from an AC line.

Another auto-ranging approach suitable for both PFC and non-PFCapplications is the use of a line frequency transformer with switchedwindings. The line voltage may be applied across all or part of theprimary winding depending on the applied line voltage. In PFCapplications the more common approach is use of a PFC boost converter asshown in FIG. 11. The off-line auto-ranging PFC power supply of FIG. 11includes bridge rectifier 501, non-isolated PFC Boost converter 507, andstorage capacitor 508, followed by isolated DC—DC converter 504. Inorder to control the current drawn from the AC line for PFC, the outputvoltage V_(B) of the boost converter must be set to a voltage greaterthan the highest peak input voltage V_(IN). In a typical power supplydesigned for international use, the boost voltage may be 400V. Power isthen converted from the boost voltage down to the load voltage by DC—DCconverter 504, which provides voltage transformation, regulation, andisolation. Operation of the boost and DC—DC converters at such highvoltages includes cost and performance penalties including, lower figureof merit for switches at high voltages and safety issues for energystorage at high voltages.

One solution, disclosed in Vinciarelli et al., “Efficient PowerConversion,” U.S. Pat. No. 5,786,992, issued Jul. 28, 1998, assigned tothe same assignee as this application and incorporated by reference,configures power converters in series and parallel allowing thecombination of converters to operate over a greater voltage range.

SUMMARY

In general, one aspect features a method of converting power from aninput source for delivery to a load, where the load may vary over anormal operating range. The method uses an array of two or more VTMswhere the array has an input for receiving power from the input sourceand an output for delivering power to the load. Each VTM has an input,an output, and a substantially fixed voltage transformation ratio,K=V_(out)/V_(in), over the normal operating range, where V_(in) is thevoltage across the respective VTM input and V_(out) is the voltageacross the respective VTM output. Each VTM provides isolation betweenits input and its output. The method adaptively configures the VTMs inand out of a series connection to adaptively adjust the aggregatevoltage transformation ratio of the array and regulate the outputvoltage.

Implementations of the method may include one or more of the followingfeatures. The inputs of the VTMs may be adaptively configured. Theoutputs of the VTMs may be adaptively configured. The VTMs may use amethod of converting power that includes forming a resonant circuitincluding a transformer and having a characteristic resonant frequencyand period. Two or more primary switches may be used to drive theresonant circuit. A switch controller may be used to operate the primaryswitches in a series of converter operating cycles. Each converteroperating cycle may be characterized by two power transfer intervals ofessentially equal duration, during which one or more of the primaryswitches are ON and power is transferred from the input of the VTM tothe output of the VTM via the transformer, and voltages and currents inthe VTM rise and fall at the characteristic resonant frequency. Eachconverter operating cycle may be further characterized by twoenergy-recycling intervals each having an essentially constant durationover the normal operating range during which the primary switches areOFF and magnetizing current may be used to charge and dischargecapacitances during the energy-recycling intervals. The switchcontroller may be used to turn the primary switches OFF essentially attimes when the current in a secondary winding returns to zero. Theadaptive configuring may be performed in response to changes sensed inthe array input voltage. The adaptive configuring may be performed inresponse to sensed changes in the array output voltage. The VTMs in thearray may have voltage transformation ratios that form a binary series.The array may include a main VTM with fixed connections to the arrayinput and output and an auxiliary VTM that is adaptively configuredbetween a series-connection with the main VTM or disconnected from thearray. A linear regulator may be used between the array output and theload. A linear regulator may be used between the input source and thearray input.

In general, another aspect features a method of converting power from aninput source for delivery to a load, where the load may vary over anormal operating range. The method uses an integrated adaptive arrayhaving an input, an output, a number, N, of input cells each having arespective number, P_(x), of turns and a number, M, of output cells eachhaving a respective number, S_(x), of turns, where N+M is greater than2. Magnetic coupling is provided between the turns to form a transformercommon to each of the input and output cells. The cells may beadaptively configured in and out of a series connection such that theturns of selected ones of the input cells are adaptively connected inseries and the turns of selected ones of the output cells are adaptivelyconnected in series to provide an adaptively adjustable transformerturns ratio, which is a function of the ratio of (a) the sum of thenumber of turns in the selected ones of the series-connected outputcells to (b) the sum of the number of turns in the selected ones of theseries-connected input cells.

Implementations of the method may include one or more of the followingfeatures. The number, M, of output cells may equal 1. The number, N, ofinput cells may equal 1. The integrated adaptive array may use a methodof converting power that includes forming a resonant circuit includingthe transformer and having a characteristic resonant frequency andperiod. Two or more primary switches may be used in at least one of theprimary cells to drive the resonant circuit. A switch controller may beused to operate the primary switches in a series of converter operatingcycles. Each converter operating cycle may be characterized by two powertransfer intervals of essentially equal duration, during which one ormore of the primary switches are ON and power is transferred from theinput of the integrated adaptive array to the output of the integratedadaptive array via the transformer, and voltages and currents in theintegrated adaptive array rise and fall at the characteristic resonantfrequency. Each converter operating cycle may be further characterizedby two energy-recycling intervals each having an essentially constantduration over the normal operating range during which the primaryswitches are OFF; and magnetizing current may be used to charge anddischarge capacitances during the energy-recycling intervals. The switchcontroller may be used to turn the primary switches OFF essentially attimes when the current in a secondary winding returns to zero. Theadaptive configuring may be performed in response to sensed changes inthe integrated adaptive array input voltage. The adaptive configuringmay be performed in response to sensed changes in the integratedadaptive array output voltage. The input or output cells may include anumber of turns that form a binary series. A main input cell having afixed connection to the integrated adaptive array input may be used. Anauxiliary input cell may be adaptively configured between aseries-connection with the main input cell or disconnected from theintegrated adaptive array input. A linear regulator may be used betweenthe integrated adaptive array output and the load. A linear regulatormay be used between the input source and the integrated adaptive arrayinput. The number N may be 2 and two of the input cells may be arrangedin a pair, each pair comprising a first input cell and a second inputcell. A positive-referenced switch and a negative-referenced switch maybe used in each of the first and second input cells to form adouble-ended drive for the respective turns. The respective turns of thefirst and second input cells may be connected to induce opposing flux inthe transformer when driven by their respective positive-referencedswitches. A controller may be adapted to operate the switches of thefirst and second input cells substantially 180 degrees out of phase suchthat the positive-referenced switch of the first input cell and thenegative-referenced switch of the second input cell are ON together andthe negative-referenced switch of the first input cell and thepositive-referenced switch of the second input cell are ON together. Thepositive-referenced switches and the negative-referenced switches mayhave a maximum voltage rating that is lower than the input voltage. Thenumber N may be a multiple of 2 and all of the input cells may bearranged in pairs. The integrated adaptive array may be an adaptive VTMarray and the adjustable transformer turns ratio may provide anadjustable voltage transformation ratio, K=V_(out)/V_(in), where V_(in)is the voltage across the integrated array input and V_(out) is thevoltage across the integrated array output.

In general, another aspect features an apparatus for converting powerfrom an input source for delivery to a load, where the load may varyover a normal operating range. The apparatus includes an array of two ormore VTMs. The array has an input for receiving power from the inputsource and an output for delivering power to the load. Each VTM has aninput, an output, and a substantially fixed voltage transformationratio, K=V_(out)/V_(in), over the normal operating range where V_(in) isthe voltage across the respective VTM input and V_(out) is the voltageacross the respective VTM output. Each VTM provides isolation betweenits input and its output. Configuration switches are connected to theVTMs for configuring the VTMs in and out of a series connection. Theapparatus configures the VTMs in and out of the series connection toadaptively adjust the aggregate voltage transformation ratio of thearray and regulate the output voltage.

Implementations of the apparatus may include one or more of thefollowing features. The configuration switches may be connected to theinputs of the VTMs and the VTM inputs may be adaptively configured. Theconfiguration switches may be connected to the outputs of the VTMs andthe VTM outputs may be adaptively configured. The VTMs may have aresonant circuit including a transformer and having a characteristicresonant frequency and period and two or more primary switches may beconnected to drive the resonant circuit. A switch controller may beadapted to operate the primary switches in a series of converteroperating cycles, each converter operating cycle characterized by twopower transfer intervals of essentially equal duration, during which oneor more of the primary switches are ON and power is transferred from theinput of the VTM to the output of the VTM via the transformer. Voltagesand currents in the VTM may rise and fall at the characteristic resonantfrequency. Each converter operating cycle may be further characterizedby two energy-recycling intervals each having an essentially constantduration over the normal operating range during which the primaryswitches are OFF. Magnetizing current may be used to charge anddischarge capacitances during the energy-recycling intervals. The switchcontroller may be adapted to turn the primary switches OFF essentiallyat times when the current in a secondary winding returns to zero. TheVTMs may be configured in response to changes in the sensed array inputvoltage. The VTMs may be configured in response to changes in the sensedarray output voltage. The VTMs may have voltage transformation ratiosthat form a binary series. The array may include a main VTM having fixedconnections to the array input and output and an auxiliary VTM beingconnected between a series-connection with the main VTM or disconnectedfrom the array via the configuration switches. A linear regulator may beconnected between the array output and the load. A linear regulator maybe connected between the input source and the array input.

In general, another aspect features an apparatus for converting powerfrom an input source for delivery to a load, where the load may varyover a normal operating range. The apparatus includes an integratedadaptive array having an input, an output, a number, N, of input cellseach having a respective number, P_(x), of turns and a number, M, ofoutput cells each having a respective number, S_(x), of turns, where N+Mis greater than 2. Magnetic coupling between the turns forms atransformer common to each of the input and output cells. Configurationswitches are connected to configure the cells in and out of a seriesconnection. The apparatus is adapted to configure the cells in and outof the series connection such that the turns of selected ones of theinput cells are adaptively connected in series and the turns of selectedones of the output cells are adaptively connected in series to providean adaptively adjustable transformer turns ratio, which is a function ofthe ratio of (a) the sum of the number of turns in the selected ones ofthe series-connected output cells to (b) the sum of the number of turnsin the selected ones of the series-connected input cells.

Implementations of the apparatus may include one or more of thefollowing features. The number, M, of output cells may equal 1 and theconfiguration switches may be connected to the input cells. The number,N, of input cells may equal 1 and the configuration switches may beconnected to the output cells. A resonant circuit may include thetransformer and have a characteristic resonant frequency and period. Twoor more primary switches in at least one of the primary cells may beadapted to drive the resonant circuit. A switch controller may beadapted to operate the primary switches in a series of converteroperating cycles. Each converter operating cycle may be characterized bytwo power transfer intervals of essentially equal duration, during whichone or more of the primary switches are ON and power is transferred fromthe input of the integrated adaptive array to the output of theintegrated adaptive array via the transformer. Voltages and currents inthe adaptive array may rise and fall at the characteristic resonantfrequency. Each converter operating cycle may be further characterizedby two energy-recycling intervals each having an essentially constantduration over the normal operating range during which the primaryswitches are OFF. Magnetizing current may be used to charge anddischarge capacitances during the energy-recycling intervals. The switchcontroller may be adapted to turn the primary switches OFF essentiallyat times when the current in a secondary winding returns to zero. Thecells may be configured in response to changes in the adaptive arrayinput voltage. The cells may be configured in response to changes in theadaptive array output voltage. The input or output cells may have anumber of turns that form a binary series. The input cells may have anumber of turns that form a first binary series and the output cells mayhave a number of turns that form a second binary series. A main inputcell may have a fixed connection to the integrated adaptive array input.An auxiliary input cell may be switched between a series-connection withthe main input cell or disconnected from the integrated adaptive arrayinput. A linear regulator may be connected between the integratedadaptive array output and the load. A linear regulator may be connectedbetween the input source and the integrated adaptive array input. Thenumber N may be at least 2 and two of the input cells may be arranged ina pair, including a first input cell and a second input cell. The firstand second input cells may each have a positive-referenced switch and anegative-referenced switch connected to form a double-ended drive forthe respective turns. The respective turns of the first and second inputcells may be connected to induce opposing flux in the transformer whendriven by their respective positive-referenced switches. A controllermay be adapted to operate the switches of the first and second inputcells substantially 180 degrees out of phase such that thepositive-referenced switch of the first input cell and thenegative-referenced switch of the second input cell are ON together andthe negative-referenced switch of the first input cell and thepositive-referenced switch of the second input cell are ON together. Theswitches may have a maximum voltage rating that is lower than the inputvoltage. N may be a multiple of 2 and all of the input cells may bearranged in pairs. The integrated adaptive array may be an adaptive VTMarray and the adjustable transformer turns ratio may provide anadjustable voltage transformation ratio, K=V_(out)/V_(in), where V_(in)is the voltage across the integrated array input and V_(out) is thevoltage across the integrated array output.

In general, another aspect features a method of converting power from aninput source at an input voltage for delivery to a load over a normaloperating range. The method includes providing a number, N, of inputcells, where N is at least 2, and arranging at least two of the inputcells in pairs, each pair including a first input cell and a secondinput cell. Each input cell has a respective number, P_(x), of turns. Anumber, M, of output cells each having a respective number, S_(x), ofturns is provided. Magnetic coupling is provided between the turns toform a transformer common to each of the input and output cells. Apositive-referenced switch and a negative-referenced switch are providedin each of the first and second input cells to form a double-ended drivefor the respective turns. The respective turns of the first and secondinput cells are connected to induce opposing flux in the transformerwhen driven by their respective positive-referenced switches. Acontroller is provided to operate the switches of the first and secondinput cells substantially 180 degrees out of phase such that thepositive-referenced switch of the first input cell and thenegative-referenced switch of the second input cell are ON together andthe negative-referenced switch of the first input cell and thepositive-referenced switch of the second input cell are ON together.

Implementations of the method may include one or more of the followingfeatures. A half-bridge configuration may be used for the first andsecond input cells. The positive-referenced switches and thenegative-referenced switches may have a maximum voltage rating that islower than the input voltage. The number of turns in the first inputcell may equal the number of turns in the second input cell. The numberM may equal 1 and the number N may equal 2. The number N may be amultiple of 2 and be greater than 2, and all of the input cells may bearranged in pairs.

In general, another aspect features an apparatus for converting powerfrom an input source at an input voltage for delivery to a load over anormal operating range. The apparatus includes a number, N, of inputcells, where N is at least 2, and at least two of the input cells arearranged in a pair. Each pair includes a first input cell and a secondinput cell and each input cell has a respective number, P_(x), of turns.The apparatus includes a number, M, of output cells each having arespective number, S_(x), of turns. Magnetic coupling is used betweenthe turns to form a transformer common to each of the input and outputcells. The first and second input cells each have a positive-referencedswitch and a negative-referenced switch connected to form a double-endeddrive for the respective turns. The respective turns of the first andsecond input cells are connected to induce opposing flux in thetransformer when driven by their respective positive-referencedswitches. A controller is adapted to operate the switches of the firstand second input cells substantially 180 degrees out of phase such thatthe positive-referenced switch of the first input cell and thenegative-referenced switch of the second input cell are ON together andthe negative-referenced switch of the first input cell and thepositive-referenced switch of the second input cell are ON together.

Implementations of the apparatus may include one or more of thefollowing features. The first and second input cells may have ahalf-bridge configuration. The positive-referenced switches and thenegative-referenced switches may have a maximum voltage rating that islower than the input voltage. The number of turns in the first inputcell may equal the number of turns in the second input cell. The numberM may equal 1 and the number N may equal 2. The number N may be amultiple of 2 greater than 2, and all of the input cells may be arrangedin pairs.

In general, another aspect features a method of converting power from asource at an input voltage for delivery to a load, where the inputvoltage may vary between a high line voltage and a low line voltage. Anintegrated converter array having an input, an output, and a first inputcell and a second input cell, each input cell having a respectivenumber, P_(x), of turns and an output cell having a respective number,S_(x), of turns is provided. Magnetic coupling is provided between theturns to form a transformer common to the first and second input cellsand the output cell. The input cells are configured in a parallelconnection for operation at the low line voltage and in a seriesconnection for operation at the high line voltage.

Implementations of the method may include one or more of the followingfeatures. Each input cell may be driven by the input voltage in theparallel connection and one-half of the input voltage in the seriesconnection. The integrated converter array may be an integrated VTMarray. The integrated VTM array may use a method of converting powerthat includes forming a resonant circuit including the transformerhaving a characteristic resonant frequency and period, and providing twoor more primary switches in at least one of the input cells to drive theresonant circuit. A switch controller may be provided to operate theprimary switches in a series of converter operating cycles characterizedby two power transfer intervals of essentially equal duration, duringwhich one or more of the primary switches are ON and power istransferred from the input of the integrated VTM array to the output ofthe integrated VTM array via the transformer. Voltages and currents inthe integrated adaptive array may rise and fall at the characteristicresonant frequency. A positive-referenced switch and anegative-referenced switch connected to form a double-ended drive forthe respective turns may be provided in each of the first and secondinput cells. The respective turns of the first and second input cellsmay be connected to induce opposing flux in the transformer when drivenby their respective positive-referenced switches. A controller may beprovided to operate the switches of the first and-second input cellssubstantially 180 degrees out of phase such that the positive-referencedswitch of the first input cell and the negative-referenced switch of thesecond input cell are ON together and the negative-referenced switch ofthe first input cell and the positive-referenced switch of the secondinput cell are ON together. The switches may have a maximum voltagerating that is lower than the high line voltage. A circuit may beprovided to sense the input voltage and to automatically configure theinput cells in the series or parallel connections in response to theinput voltage. The integrated converter array may be an integrated DC—DCconverter array with regulation circuitry to regulate the output.

In general, another aspect features a method of converting power from anAC line at a line voltage for delivery to a load at a DC output voltage,where the line voltage may vary between a high line voltage and a lowline voltage. The AC line may be passed through a rectifier to produce arectified line signal at a rectified voltage. At least two input cellseach having at least one switch for driving a primary winding forconverting power received from the rectified line signal may beprovided. An output cell having a secondary winding magnetically coupledto the primary winding may be provided in each of the input cells. Theoutput cell may have rectification circuitry for delivering a unipolaroutput voltage. The input cells may be connected in series for operationat the high line voltage to divide the rectified voltage between theinput cells.

Implementations of the method may include one or more of the followingfeatures. Capacitive energy storage may be provided between the unipolaroutput voltage and the load. The input cells may be configured in aparallel connection for operation at the low line voltage to divide aninput power between the input cells. Regulation circuitry may beprovided between the unipolar output voltage and the load. A powerfactor correction circuit may be provided between the DC bus voltage andthe capacitive energy storage. The capacitive energy storage may beprovided at the output of the rectification circuitry. The capacitiveenergy storage may be provided at the load. A controller that senses theAC line voltage may be provided to configure the input cells in serieswhen the AC line voltage is within an upper range and in parallel whenthe AC line voltage is within a lower range. The peak value of therectified AC line voltage may be sensed. The peak value may be comparedto a predetermined switchover threshold. The upper range may be between226 V PEAK and 388 V PEAK. The lower range may be between 113 V PEAK and195 V PEAK. The switchover threshold may be 250 V PEAK. The switchoverthreshold may be greater than voltages within the lower range.

In general, another aspect features an apparatus for converting powerfrom a source at an input voltage for delivery to a load, where theinput voltage may vary between a high line voltage and a low linevoltage. The apparatus may include an integrated converter array havingan input, an output, and a first input cell and a second input cell,each input cell having a respective number, Px, of turns and an outputcell having a respective number, Sx, of turns. Magnetic coupling betweenthe turns may form a transformer common to the first and second inputcells and the output cell. Configuration switches may be connected toconfigure the input cells in a parallel connection for operation at thelow line voltage and in a series connection for operation at the highline voltage.

Implementations of the method may include one or more of the followingfeatures. Each input cell may be essentially driven by the input voltagein the parallel connection and one-half of the input voltage in theseries connection. The integrated converter array may be an integratedVTM array. A resonant circuit may include the transformer and have acharacteristic resonant frequency and period. At least one of the inputcells may include two or more primary switches adapted to drive theresonant circuit. A switch controller may be adapted to operate theprimary switches in a series of converter operating cycles. Eachconverter operating cycle may be characterized by two power transferintervals of essentially equal duration, during which one or more of theprimary switches are ON and power is transferred from the input of theintegrated VTM array to the output of the integrated VTM array via thetransformer, and voltages and currents in the integrated adaptive arrayrise and fall at the characteristic resonant frequency. The first andsecond input cells may have a positive-referenced switch and anegative-referenced switch connected to form a double-ended drive forthe respective turns. The respective turns of the first and second inputcells may be connected to induce opposing flux in the transformer whendriven by their respective positive-referenced switches. A controllermay be adapted to operate the switches of the first and second inputcells substantially 180 degrees out of phase such that thepositive-referenced switch of the first input cell and thenegative-referenced switch of the second input cell are ON together andthe negative-referenced switch of the first input cell and thepositive-referenced switch of the second input cell are ON together. Theswitches may have a maximum voltage rating that is lower than the highline voltage. The apparatus may include a circuit may be adapted tosense the input voltage and to automatically configure the input cellsin the series or parallel connections in response to the input voltage.The integrated converter array may be an integrated DC—DC converterarray with regulation circuitry adapted to regulate an output of theintegrated array.

In general, another aspect features an apparatus for converting powerfrom an AC line at a line voltage for delivery to a load at a DC outputvoltage, where the line voltage may vary between a high line voltage anda low line voltage. A rectifier may have an input connected to the ACline to produce a rectified line signal at a rectified voltage. Theapparatus may include at least two input cells each having at least oneswitch for driving a primary winding for converting power received fromthe rectified line signal. An output cell may have a secondary windingmagnetically coupled to the primary winding in each of the input cellsand rectification circuitry for delivering a unipolar output voltage.The apparatus may be adapted to configure the input cells in series foroperation at the high line voltage to divide the rectified voltagebetween the input cells.

Implementations of the method may include one or more of the followingfeatures. Capacitive energy storage may be connected between theunipolar output voltage and the load. The apparatus may be adapted toconfigure the input cells in a parallel connection for operation at thelow line voltage to divide an input power between the input cells. Theapparatus may include regulation circuitry having an input connected toreceive power from the unipolar output voltage and an output fordelivering power to the load. A power factor correction circuit may havean input connected to receive power from the DC bus voltage and anoutput for delivering power to the capacitive energy storage. Thecapacitive energy storage may be connected across the output of therectification circuitry. The capacitive energy storage may be connectedacross the load. A controller may be adapted to sense the AC linevoltage and to configure the input cells in series when the AC linevoltage is within an upper range and in parallel when the AC linevoltage is within a lower range. The controller may be adapted to sensethe peak value of the rectified AC line voltage. The controller may beadapted to compare the peak value to a predetermined switchoverthreshold. The upper range may be between 226 V PEAK and 388 V PEAK. Thelower range may be between 113 V PEAK and 195 V PEAK. The switchoverthreshold may be 250 V PEAK. The switchover threshold may be greaterthan voltages within the lower range. Each input cell may have a voltagetransformation ratio, K=4.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows an input-switched adaptive array of VTMs.

FIG. 2 shows an output-switched adaptive array of VTMs.

FIG. 3 shows a schematic diagram of a full-bridge SAC.

FIG. 4 shows a schematic diagram of a modified SAC with an adaptivearray of input cells integrated with a common output circuit.

FIGS. 5A and 5B show use of a linear regulator with an adaptive array ofVTMs.

FIG. 6 shows a schematic diagram of an array of VTM cells with theinputs and outputs adaptively configured in series to provide outputregulation.

FIG. 7 shows a schematic of an output switched adaptive array of VTMs.

FIG. 8 shows a converter topology using a complementary pair of inputcells.

FIG. 9 shows an off line auto-ranging converter module topology withcomplementary half-bridge SAC input cells.

FIG. 10 shows a prior art off-line auto-ranging power supply.

FIG. 11 shows a prior art off-line auto-ranging power supply with powerfactor correction.

FIG. 12 shows an off-line auto-ranging power supply using anauto-ranging converter module cascaded with a power factor correctedpower regulator module.

FIG. 13 shows an off-line auto-ranging power supply using auto-rangingconverter modules cascaded with a power regulator module for use with athree-phase line.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

A Voltage Transformation Module (“VTM”) as defined herein delivers a DCoutput voltage, V_(out), which is a fixed fraction of the voltage,V_(in), delivered to its input and provides isolation between its inputand its output. The voltage transformation ratio or voltage gain of theVTM (defined herein as the ratio, K=V_(out)/V_(in), of its outputvoltage to its input voltage at a load current) is fixed by design, e.g.by the VTM converter topology, its timing architecture, and the turnsratio of the transformer included within it. Vinciarelli, “FactorizedPower Architecture With Point Of Load Sine Amplitude Converters,” U.S.patent application Ser. No. 10/264,327, filed Oct. 1, 2002, (referred toherein as the “Factorized Application”) assigned to the same assignee asthis application and incorporated by reference, discloses preferredconverter topologies and timing architectures for VTMs, which will begenerally referred to as a Sine Amplitude Converter (“SAC”) topology.

The SAC topology has many advantages over prior art DC-to-DC transformertopologies. The SAC topology may incorporate a “low Q” resonant tank(where the term “low Q” has the meaning given in the FactorizedApplication with respect to transformers for use in a SAC) and isnominally operated at resonance so that the reactive impedances of theelements of the resonant tank cancel each other out. The SAC uses aresonant topology at resonance so that the impedance of the resonantcircuit becomes essentially resistive, minimizing the output impedanceand open-loop resistance of the converter, and thus minimizing open-loopvoltage droop as a function of changing load. Greater consistency inopen-loop DC output resistance, owing to the elimination of dependencyon reactive impedances, gives rise to fault tolerant power sharingattributes which are particularly desirable in applications in whichmultiple, paralleled, VTMs are operated as a power sharing array.

Operating waveforms in SAC converters closely approximate puresinusoidal waveforms, thus optimizing spectral purity, and hence theconverter's conducted and radiated noise characteristics. In operation,a SAC maintains an essentially constant conversion ratio and operatingfrequency as the amplitudes of its essentially sinusoidal voltage andcurrent waveforms vary in response to a varying output load. The timingarchitecture of the SAC topology supports ZVS operation of the primaryswitches and ZCS and ZVS operation of the secondary switches, virtuallyeliminating switching losses in the primary switching elements andsecondary switching elements, or rectifiers, particularly synchronousrectifiers, enabling higher switching frequencies and higher converterpower density and efficiency. Sine Amplitude Converters provide the bestcombination of attributes to support the requirements of VTMs and highperformance DC—DC converters.

VTMs and in particular SACs are capable of achieving very high powerdensities. The present application discloses methods and apparatus foradaptively configuring an array of VTMs, as the input voltage to thearray of VTMs varies over a pre-defined range, in order to regulate theoutput voltage of the array.

A “digital” ladder array of VTMs 100 adaptively configurable to providea regulated output voltage from an input source 10 is shown in FIG. 1.The adaptive VTM array 100 adjusts to changes in input voltage orchanging output voltage requirements by selectively configuring theVTMs. The VTM outputs are connected in parallel to supply power to theload 20. Each VTM has a transformation ratio, K, selected to provide thenecessary resolution. In the example of FIG. 1, VTMs 101, 102, 103, 104,and 105 have transformation ratios of 1/16, 1/8, 1/4, 1/2, and 1/1,respectively for a digital ladder (thus the reference to the array as a“digital” array). The VTM inputs are connected to receive power from theinput source through controlled switches 110–119 which may be lowresistance (FET) switches. The array 100 of FIG. 1 may be configured foran aggregate transformation ration of 1/1 to 1/31 in steps of 1 in thedenominator by switching the VTM inputs in and out of the input circuit.A VTM is disconnected in FIG. 1 by closing its respective shunt switch(110–114) and opening its respective series switch (115–119). The VTMsthat are disconnected may be disabled (i.e., rendered non-operating)until switched back into the circuit or may remain enabled. A ladderswitch controller 106 senses the input voltage and configures the ladderswitches to provide the necessary aggregate voltage transformation ratioto regulate the load voltage. The controller 106 may also sense the loador array output voltage as shown in FIG. 1.

The input voltage will divide across the series connected inputs of VTMshaving their outputs connected in parallel in proportion to theirrespective individual transformation ratios. The voltage across theinput of VTM_(n) (in a series-connected-input andparallel-connected-output array) may be expressed as follows:

$V_{i_{n}} = {\frac{V_{Source}}{K_{n}} \times K_{aggr}}$where K_(aggr), the aggregate transformation ratio for theseries-connected-input and parallel-connected-output array of VTMs, isthe reciprocal of the sum of the individual transformation ratios ofthose VTMs that are connected in the array:

$K_{aggr} = {1/{\sum\limits_{connected}\frac{1}{K_{i}}}}$

Referring to the example of FIG. 1, assume that the array 100 is todeliver a nominal 2.3V to the load 20 from an input source 10 that mayvary from 36V to 72V. At low line conditions with Vin=36V, thecontroller configures the switches (110, 116–119 open and 115, 111–114closed) so that only the input of VTM 101 is connected across the inputsource and the other VTMs 102–105 are disconnected from the source.Since the only connected VTM is the one having K₁=1/16, the aggregatetransformation ratio will be K_(aggr)=1/16 and the array will deliverV_(out)=V_(Source)K_(aggr)=36/16=2.25V to the load. As the sourcevoltage increases, the controller adaptively reconfigures the array toprovide the necessary load regulation. For example, for a source voltageof 38V, the controller may reconfigure the array by connecting theinputs of VTMs 101 and 105 in series and disconnecting VTMs 102–104(switches 110, 114, 116–118 open, 111–113, 115, 119 closed) to providean aggregate transformation ratio K_(aggr)=1/(16+1)=1/17 and an outputvoltage V_(out)=V_(Source)K_(aggr)=38/17=2.24V. At maximum inputvoltage, with Vin=72V, controller 106 configures the switches (110–114open, 115–119 closed) to connect all of the VTMs in series. Theaggregate transformation ratio will be K_(aggr)=1/(16+8+4+2+1)=1/31 andthe array will deliver 72/31=2.32V to the load.

It will be appreciated that the adaptive digital ladder VTM array ofFIG. 1 efficiently provides all of the classic functions of a DC—DCconverter (including isolation, voltage step-up or step down, ANDregulation) by adaptively configuring a series combination of VTM inputsto adjust the aggregate K factor, K_(aggr). The number of VTMs in thearray may be increased to provide greater resolution and thus betterregulation. For example, an additional VTM (e.g., one having atransformation ratio K=2/1 or one having a transformation ratio K=1/32)may be added to further increase the resolution or the input range ofthe array. However, the minimum input or output operating voltage of theVTMs may impose a practical limitation on the resolution in the K, 2K,4K digital ladder array of FIG. 1 because of practical limitations inachievable values of K in a VTM.

If the output voltage regulation requirement exceeds the resolution ofan adaptive VTM array, finer regulation may be provided by an analogdissipative linear regulator in series with the input or output of a VTMarray. FIGS. 5A and 5B, show a linear regulator 107 in series with theoutput and input, respectively, of adaptive array 100. If, for example,an adaptive VTM array can achieve a regulation resolution of 1 percentwith a manageable number of bits, the dissipation associated with usingan appropriately designed analog series linear regulator, e.g. 107, toabsorb substantially all of the 1% VTM array error may be negligible interms of the overall converter efficiency. In fact such a loss may besmaller than the loss associated with a series-connected switchingregulator (e.g., a “PRM”, as described in the Factorized Application,and that may, in some applications, use the topology described inVinciarelli, “Buck-Boost DC—DC Switching Power Conversion,” U.S. patentapplication Ser. No. 10/214,859, filed Aug. 8, 2002, both assigned tothe same assignee as this application and incorporated by reference).Use of a series linear regulator also eliminates the response delays andswitching noise that would be introduced by use of a series-connectedswitching regulator. The analog series linear regulator also may provideenough bandwidth to effectively filter “hash” or “digital jitter” thatmay be generated due to instances of reconfiguration of the array.

It may be preferable to provide the configuration switches on the highervoltage side of the array to reduce power dissipation in the switches.In the example of FIG. 1, the source voltage was stepped down by thearray; therefore, the switches were placed on the input side of thearray. In voltage step-up applications, the switches may be placed onthe secondary side to produce a series connected secondary adaptivearray.

Referring to FIG. 2, an example of a step-up adaptive array 150 withconfiguration switches 161–164, 166–169 on the output side of the arrayis shown. The array 150 is designed to provide 48+/−1 Volt output froman input voltage range of 10–15V. For this application, the array mustprovide a minimum transformation ratio less than or equal to K_(min):

$K_{\min} = {\frac{V_{{out}_{\max}}}{V_{{in}_{\max}}} = {\frac{48 + 1}{15} = 3.26}}$The array must also provide a transformation ratio greater than or equalto K_(max):

$K_{\max} = {\frac{V_{{out}_{\min}}}{V_{{in}_{\min}}} = {\frac{48 - 1}{10} = 4.7}}$In order to satisfy the regulation requirement, the array must have astep size in the transformation ratio less than or equal to ΔK_(max):

${\Delta\; K_{\max}} = {\frac{\Delta\; V_{out}}{V_{{in}_{\max}}} = {\frac{49 - 47}{15} = {.13}}}$Finally, the array must provide a number of steps in the transformationratio greater than or equal to N_(steps):

$N_{steps} = {\frac{K_{\max} - K_{\min}}{\Delta\; K_{\max}} = {\frac{4.7 - 3.26}{.13} = 11.1}}$From the above calculations, a five VTM array will satisfy the designcriteria. A four-bit K, 2K digital ladder having 15 steps will satisfythe N_(steps) requirement. A step size of ΔK=1/8=0.125 is less than andtherefore satisfies the resolution requirement ΔK_(max) and provides anadjustment range N_(steps)×ΔK=15×1/8=1.875 that is greater thanrequired. VTMs 152, 153, 154, and 155 will have the following respectivetransformation ratios K₅=1/8, K₄=1/4, K₃=1/2, and K₂=1. Thetransformation ratio of the main VTM 151 thus may be set to K₁=3 whichwill easily satisfy the minimum requirement, K_(min) and provide anaggregate transformation ratio for the array ranging from 3.0 to 4.875.

The inputs of the VTMs 151–155 are connected in parallel and the outputsare adaptively connected in series as needed to regulate the outputvoltage. Because the main VTM 151 is configured to deliver powercontinuously it does not have a series or shunt switch on its output(the array of FIG. 1 may also be adapted in this way). Auxiliary VTMs152–155 are configured to form the four-bit K, 2K ladder whose switchesare controlled by the ladder switch controller 156. The controller maysense the source and load voltages to better regulate the load voltage.It will be appreciated that array 150 provides 48V+/−2% over an inputvoltage range from 9.6V to 16.3V.

An example of an adaptive array comprising a power sharing sub-array ofVTMs is shown in FIG. 7. The adaptive array 180 is designed to deliver50 VDC+/−5V from an input source that varies from 38 to 55 VDC. A powersharing sub-array 181, comprising VTMs 181A–181E, each having atransformation ratio K=1, supplies most of the power to the load. As theinput voltage drops, the outputs of auxiliary VTMs 182–184, each ofwhich has a transformation ratio of K=1/8, are switched in series withthe output of the main array 181 by ladder switch controller 185. Theaggregate transformation ratio of the adaptive array 180 varies fromK_(aggr)=1 to 1.375 providing the necessary regulation. The auxiliaryVTMs supply only a small fraction of the total power and therefore donot need to be connected in power sharing arrays for this application.

As described in conjunction with FIGS. 1–2 and 7, the adaptive VTM arrayconcept may be realized with a multiplicity of separate VTMs havingindependent isolation transformers and appropriate K factors, with eachsuch VTM separately controlled to operate at a respective switchingfrequency. However, the Sine Amplitude Converter (“SAC”) is particularlywell suited for use in an integrated version of an adaptive VTM array. Afull-bridge SAC of the type described in the Factorized Application isshown in FIG. 3. The SAC includes one primary circuit and one secondarycircuit. The primary circuit comprises transformer primary windingW_(P), in series with resonant capacitance C_(R), and resonantinductance L_(R) (which may have a low Q (where the term “low Q” has themeaning given in the Factorized Application with respect to transformersfor use in a SAC) and may partially or entirely consist of the primaryreflected leakage inductance of the transformer) driven by primaryswitches SW1, SW2, SW3, SW4. The switches SW1, SW2, SW3, SW4, arecontrolled by the switch controller to operate at near resonance withshort energy recycling intervals to provide zero voltage switching. Theoutput circuit, which includes the transformer secondary winding W_(P),coupled to a rectifier circuit and a filter capacitor, supplies power tothe load.

Referring to FIG. 4, an integrated adaptive array 200 using the SACtopology is shown having a plurality of full-bridge SAC input cells 201,202, 203, 204 coupled to a common SAC output cell 208. The input cellsmay be the same as the primary circuit of FIG. 3 with the addition of abypass capacitor, e.g. capacitors 212 and 222, a series switch, e.g.series switches 211, 222, and a shunt switch, e.g. shunt switch 210, 220for each cell. Also the primary windings W_(P1), W_(P2), W_(P3), . . .W_(Pm) may be part of one transformer 205 having a single secondarywinding W_(S) coupled to the output circuit 208. The number of turns N₁,N₂, N₃, . . . N_(m) in the primary windings may be selected to providethe appropriate transformation ratio for each cell. Using the K, 2Kdigital ladder example of FIG. 1, the integrated adaptive array SAC 200could have five input cells having respectively 16 turns, 8 turns, 4turns, 2 turns and 1 turn. A resonant switch controller 207 common toall of the cells may operate the primary switches SW1–SW4 of all of thecells (and the synchronous rectifiers in the output cells if used) insynchronism.

The input cells are switched in and out of the series combination asrequired to adjust the aggregate transformation ratio and thus regulatethe output voltage as discussed above in connection with FIG. 1. When aninput cell is in the circuit, its series switch e.g. 211, 221 is closedand its shunt switch e.g. 210, 220 is open. Conversely, when an inputcell is switched out of the circuit its series switch e.g. 211, 221 isopen and its shunt switch e.g. 210, 220 is closed. The ladder switchcontroller 205 controls the series and shunt switches of all of thecells. An input cell that is switched out of the circuit may remainactive (i.e., its primary switches continue to operate) which will keepits respective bypass capacitor, e.g. capacitor 212, 222, charged to theappropriate voltage (due to the bi-directional nature of the SACtopology) thereby eliminating in-rush current problems duringreconfiguration of the digital ladder. The ladder switch controller 206may sense the input voltage and optionally may also sense the loadvoltage to configure the input cells. When in connected in series, eachinput cell shares in a fraction of the input voltage equal to the numberof its primary winding turns divided by the total number of turns forall of the input cells that are connected in the array (i.e., where theterm “connected” refers to cells whose shunt switches are open and whoseseries switches are closed).

A more elaborate integrated adaptive array 250 may incorporate aplurality of input cells and a plurality of output cells as shown inFIG. 6. In FIG. 6, a series of VTM input cells are adaptively stacked onthe input (by means of primary series switches 315 a–315 n and primaryshunt switches 310 a–310 n analogous to, respectively, switches 115–119and 110–115 in FIG. 1) and a series of VTM output cells are adaptivelystacked on the output (by means of secondary series switches 366 a–366 mand secondary shunt switches 361 a–361 m analogous to, respectively,switches 166–169 and 161–164 in FIG. 2) to adaptively adjust theeffective VTM K factor. Because a common transformer 305, comprisingprimary windings P₁–P_(n) and secondary windings S₁–S_(m), is used forall of the cells, any combination of input and output cells may becombined to provide the requisite transformation ratio. In general, theintegrated adaptive array of FIG. 6, provides an aggregate K expressedas:K _(aggr)=(S ₁ +S ₂ + . . . +S _(m))/(P ₁ +P ₂ + . . . +P _(n))

corresponding to a truncated series combination of connected outputcells having S_(x) transformer turns and a truncated series combinationof connected input cells having P_(x) transformer turns, where the term“connected” has the definition given above). As discussed above, theintegrated adaptive array adjusts to changes in input voltage orchanging output voltage requirements by adaptively configuring the inputand/or output cells in series. It will be appreciated that thegeneralized adaptive array of FIG. 6 may be modified to use a singleinput cell with a plurality of output cells (analogous to the VTM arrayof FIG. 2) or alternatively a single output cell with a plurality ofinputs cells (as discussed above in connection with FIG. 4).Furthermore, some cells in such an array may be permanently connectedand not include series and shunt switches.

An integrated adaptive array based upon the SAC converter topology, suchas the arrays shown in FIGS. 4 and 6, may preserve all of the key SACfeatures, including, in particular: a) the benefits of low Q resonanttransformers for efficient high frequency power processing (where theterm “low Q” has the meaning given in the Factorized Application withrespect to transformers for use in a SAC); b) extremely high powerdensity (exceeding or of the order of 1KW/in³); c) absence of serialenergy storage through an inductor (as required by classic switchingregulators) leading to fast (<<1 microsecond) transient response; d)fast bi-directional power processing leading to effective bypasscapacitance multiplication; and e) low noise performance owing to theZCS/ZVS characteristics of SACs. Additional advantages, such as reducedsize and cost may be realized by integrating the array a single packageusing, e.g., the packaging and transformer design and layout techniquesdescribed in the Factorized Application; in Vinciarelli et al, “PowerConverter Package and Thermal Management,” U.S. patent application Ser.No. 10/303,613, filed Nov. 25, 2002; and in Vinciarelli, “PrintedCircuit Transformer,” U.S. patent application Ser. No. 10/723,768, filedNov. 26, 2003, all assigned to the same assignee as this application andincorporated by reference.

FIG. 8 shows an array 320 comprising two half-bridge input cells 321,322 connected in series to receive power from an input source 340 havinga voltage, V₁. Primary windings 331, 332 (having P₁ and P₂ turnsrespectively) and secondary winding 333 (having P₂ turns) form part of acommon transformer. Each input cell includes a positive-referencedswitch 324, 328 and a negative-referenced switch 326, 330 providingdoubled-ended drive for primary windings 331, 332. The input cells 321,322 are arranged in a pair with the polarity of the primary windingsreversed. The pair of input cells 321, 322 produces opposing flux whendriven by their respective positive-referenced switch 324, 328. Inoperation, the switches in the pair of input cells are operated 180degrees out of phase in synchronism so that switches SW1 324 and SW4 330are closed at essentially the same time (when switches SW2 326 and SW3328 are open) and switches SW2 326 and SW3 328 are closed at essentiallythe same time (when switches SW1 324 and SW4 330 are open).

One benefit of the complementary pair of input cells is that common-modecurrents that would otherwise be capacitively coupled between primarywindings, 331, 332, and secondary winding, 333, as illustrated by theflow of current I_(CM) between primary 340 and secondary 342 grounds inFIG. 8, will be reduced. In illustration, FIG. 8 incorporates severalrepresentative parasitic capacitances, C_(P1) through C_(P4) 334–337.When switches SW2 and SW3 are opened, the rate-of-change of voltageacross parasitic capacitors C_(P1) 334 and C_(P2) 335 will be positiveand the rate-of-change of voltage across parasitic capacitors C_(P3) 336and C_(P4) 337 will be negative and the net flow of current in thecapacitors will tend to cancel. Likewise, the currents in the parasiticcapacitors will also tend to cancel when switches SW1 and SW4 areopened. The net common-mode current, I_(CM), flowing between the primaryand secondary side of the array can be reduced using this arrangement.

Another advantage of the topology of FIG. 8 is that, for a given inputsource 345 voltage, V₁, the use of a pair of input cells allows use ofprimary switches (e.g., switches SW1–SW4, FIG. 8) having a breakdownvoltage rating that is one-half of the rating that would be required ifa single input cell were used. In one aspect, lower voltage primaryswitches (e.g. MOSFETs) may generally have lower levels of energy storedin the parasitic switch capacitances allowing the peak value ofmagnetizing energy to be set to a lower value while still enablingzero-voltage switching. For a given conversion efficiency, a reductionin magnetizing energy and current may enable operation at a higherfrequency leading to higher power density and a smaller size for theconverter. On the other hand, for a given operating frequency, areduction in magnetizing current may provide for higher conversionefficiency. In another aspect, the use of a pair of input cells in placeof a single input cell may allow use of lower cost, higher performanceswitches. For example, in “off-line” applications the input sourcevoltage, V₁, may be 370 VDC. In such applications use of a pair of inputcells enables use of primary switches having a 200 V breakdown rating,in contrast to the 400 V primary switch rating that would be required inan application using a single input cell.

Referring to FIG. 12, an auto-ranging off-line power supply topology isshown including a full-wave rectifier (in this case a bridge rectifier)501, an auto-ranging converter module (“ACM”) 400, and a power regulatormodule 509. The ACM 400, which is discussed in more detail below inconnection with FIG. 9, provides auto-ranging, voltage transformation,and isolation and may optionally provide regulation. The voltage, V₂, atthe output of the rectifier 501 is a function of the AC input voltage,V_(IN), and may therefore vary over a large range. For example, inauto-ranging off-line applications the RMS line voltage may vary between85 and 275 VAC, RMS, corresponding to peak rectified line voltages inthe range of 120V to 389V. In another application example, the RMS linevoltage may vary over a narrower range between 100V and 240V. The ACM400 may be configured to transform the relatively high peak rectifiedline voltage, V₂, to a relatively lower voltage, V₃, (e.g. having a peakvalue of 50V) allowing downstream capacitive energy storage, regulation,and PFC to be provided at the lower voltage. Better figure of meritswitches may be used in the PFC and regulation circuitry while energystorage at the lower voltage may be safer.

Referring to FIG. 9, an integrated VTM array is shown adapted to providethe ACM functions of off-line auto-ranging voltage transformation andisolation. As shown in the figure, the ACM 400 includes two half-bridgeinput cells 401 and 402 and output cell 403 based upon the SAC convertertopology. Preferably, the input cells may be complementary as discussedabove in connection with FIG. 8. The input cells 401, 402 includeprimary windings 416, 426 magnetically coupled to secondary winding 436.In the embodiment shown, the input cells include a series resonantcircuit including the primary winding and a resonant capacitor 417, 427.Primary switches 414, 415 and 424, 425 drive the resonant circuit withone half of the voltage applied across the cell input terminals 410, 411and 420, 421. Capacitors 418, 419 and 428, 429 are scaled to providefiltering on a time scale that is large relative to the resonantfrequency and small relative to the line frequency. Alternatively,full-bridge topologies may be used, eliminating capacitors 418, 419 and428, 429 and replacing them with switches. Output circuitry 430connected to the secondary winding 436 rectifies the secondary voltageand supplies a DC output voltage Vo for delivery to a load (not shown).A switching control circuit 405 operates the primary switches in aseries of converter operating cycles using gate drive transformers 412,413, and 422, 423 to turn the primary switches ON and OFF. Power for theswitching control circuit, at a relatively low voltage, V_(BIAS), may bederived from the input voltage, V_(IN), through an auxiliary windingcoupled to the input cells.

A configuration controller 404 is used to connect the input cells 410,402 in a series and a parallel configuration to provide an auto-rangingfunction. A gate bias voltage is supplied from the gate drivetransformer 422 of input cell 402 through diode 452. The gate biasvoltage is sufficient, e.g. several volts, to ensure that transistor 424is pulsed ON fully. As shown the gate bias voltage is referenced to thesource of transistor 424. When transistor 424 is ON, its source terminalis essentially tied to the positive input terminal 420 causing the gatebias voltage to be referenced to the positive input terminal 420 ofinput cell 402. Terminal 420 will be essentially at V_(IN) for theparallel connection and at V_(IN)/2 for the series connection. The gatebias voltage will provide sufficient drive to transistor 447 to ensurethat it is fully ON in the parallel configuration.

With a sufficiently large positive voltage V_(cont) applied to thecontrol terminal 440, transistor 442 is OFF and transistor 441 is ON,driving the gate of transistor 444 positive and turning transistor 444ON. Transistor 441 pulls the base of transistor 448 and the gate ofp-channel MOSFET transistor 446 low, turning transistor 448 OFF andtransistor 446 ON. With the gate bias voltage several volts above inputterminal 420 and with transistor 446 ON, the gate of transistor 447 isdriven above the source of transistor 447 turning it ON. Withtransistors 444, 446, and 447 ON, the input cells are connected inparallel across the input voltage, Vin. The parallel connection of theinput cells allows each cell to share in the power delivered by theoutput cell 403 reducing the current carried by the primary switches.

While the voltage at the control terminal 440 remains below apredetermined threshold (e.g., below a value that causes the gatevoltage of transistor 444 to drop below its gate threshold voltage),transistor 442 remains ON and transistor 441 remains OFF; transistor 448turns ON holding the gate to source voltage of transistor 446 near zerokeeping transistor 446 OFF. With transistors 446 and 444 OFF, transistor447 will be OFF. With transistors 444, 446, and 447 OFF, the input cellsare connected in series (through diode 445) across the input voltage,Vin. The series connection of the input cells divides the input voltagebetween the input cells reducing the voltage requirements of the primaryswitches.

Preferably, the peak line voltage may be sensed and used to set andlatch the control signal V_(cont) to prevent the integrated VTM arrayfrom reconfiguring the input cells as the voltage changes throughout theAC cycle. Alternatively, the configuration may be switched during the ACcycle for example when more than 2 input cells are provided. Circuitryfor sensing the peak line voltage and delivering control signal V_(cont)may be included in switching control circuit 431.

Although the ACM of FIG. 9 is shown using an integrated VTM array basedupon the SAC topology, an ACM comprising an integrated converter arraybased upon other VTM or hybrid VTM-regulating topologies (e.g., PWM VTMsand PWM regulators) may also be used. For example, an integrated VTMarray based upon a hard-switching PWM VTM topology having 2 input cells,an output cell, and a common transformer may be realized by omitting theresonant capacitors 417, 427 in FIG. 9. Alternatively, an ACM withregulation may be may realized using an integrated DC—DC converter arrayin which two or more primary cells are coupled through a commontransformer to an output circuit. Although there may be an efficiencyand EMI penalty as compared to the SAC topology, the integratedhard-switching PWM VTM array and the integrated DC—DC converter arraymay still provide some of the benefits of reduced voltage and currentstresses on the primary switches.

In FIG. 12, the power regulator module (“PRM”) connected to the outputof the ACM 400 provides regulation for the power delivered to the load505. Because the peak input voltage to the PRM is relatively low e.g.,below 50 volts, and varies over a relatively narrow range, e.g. +/−25%,the PRM may use low voltage switches providing a higher figure of meritdue to lower ON resistances and reduced gate capacitance. Because theACM provides isolation, the PRM is preferably non-isolated, thusallowing further improvement in power density. Whereas a capacitivevoltage doubler requires two bulk storage capacitors, only a single bulkstorage capacitor, at the output of the PRM, is required in a systemusing an auto-ranging ACM. Additionally, for ACMs based upon a VTMarchitecture, the PRM may provide PFC (e.g., by controlling the PRM sothat its input current approximately follows the sinusoidal waveform ofthe rectified input source) at a relatively low voltage, for examplebelow 50 Volts, instead of at 400 Volts, as is typical in off-linesystems. Because the energy density of commercially available filtercapacitors rated at 50 volts and 400 volts are comparable, storingenergy at the lower, isolated, voltage provides greater safety withvirtually no impact on power density. In very low voltage applications,the auto-ranging VTM may step the line voltage down to 3–5 Volts andsuper capacitors may be used for energy storage. Although PFC may notgenerally be required in low power (e.g., less than 200 watt) systems,it may be provided in the ACM topology without the size and costpenalties of prior art systems.

In a preferred embodiment, an ACM may be operated over a total AC inputline range of 80 VAC RMS to 275 VAC RMS (corresponding, e.g., tooperating off both a nominal 110 VAC RMS line that varies over a lowinput line range from 80 VAC RMS to 138 VAC RMS, and a nominal 220 VACRMS line that varies over a high input line range from 160 VAC RMS to275 VAC RMS). When operating from the low input line range, the peakrectified voltage at the input to the ACM may vary over a range from 113V PEAK to 195 V PEAK; when operating from the high input line range, thepeak rectified voltage at the input to the ACM may vary over a rangefrom 226 V PEAK to 388 V PEAK. Each of the input cells 410, 402 may havea K factor of 4. When the input cells are configured in series, theeffective K factor will be 8; when the input cells are configured inparallel the effective K factor will be 4.

The “switchover threshold” of such an ACM may be set to be in thenominal center of the range of peak voltages, e.g. at 250 V PEAK. Whenoperating from the low input line range, the peak rectified voltage atthe input to the ACM will be lower than the switchover threshold, thecontrol signal V_(cont) will be set high, the input cells 401, 402 willbe in parallel, the effective K factor will be 4 and the peak voltage atthe output of the ACM will vary over a range between 28.3 VPEAK and 48.8VPEAK; when operating from the high input line range, the peak rectifiedvoltage at the input to the ACM will be higher than the switchoverthreshold, the control signal V_(cont) will be set low, the input cells401, 402 will be in series, the effective K factor will be 8 and thepeak voltage at the output of the ACM will vary over a range between28.3 VPEAK and 48.5 VPEAK. As a result, as the rectified input voltageto the ACM varies between 113 V PEAK and 388 V PEAK, the output of theACM will deliver a voltage that varies approximately +/−27% about anominal peak voltage of 38.5 V PEAK. In many commercial applications,such as AC adapters for notebook computers, the RMS line range isspecified to be narrower (e.g., 100 VAC RMS to 240 VAC RMS), therectified input voltage to the ACM will be narrower and the output ofthe ACM will vary less than +/−27%.

When operated from an AC line, the input to the VTM will be atime-varying waveform that varies between zero volts and the peakvoltage of the AC line, at twice the frequency of the AC line. A VTM isgenerally capable of transforming input voltages essentially down tozero volts, provided that its internal control circuitry remainsoperational throughout the entire rectified line cycle. In preferred ACMembodiments, sufficient holdup (e.g., 10 msec) is provided in theV_(BIAS) supply so that the switching control circuit 431 remainspowered, and capable of driving the ACM switches, even as the rectifiedinput voltage to the ACM goes to zero volts.

The ACM topology may provide even greater power density and savings inthree-phase off-line applications. Referring to FIG. 13, an example ofan ACM delta configuration is shown. Three ACMs 400A–400C are connectedvia full-wave rectifiers 501A–501C between each of the three lines.Although a delta configuration is shown, the system may also beconnected in a star or wye configuration. In either case, the outputs ofthe three ACMs may be connected in parallel to feed a single PRM or aparallel array of PRMs which may also provide PFC. This configurationhas the advantage of maximizing the utility of PRMs increasing the powerdensity even further.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, it is not required that resonant capacitances C_(R) andinductances L_(R) be included in each of the SAC input cells, as isshown in FIG. 4; it is only necessary that at least one resonantcapacitance and resonant inductance be provided (see, e.g., theintegrated array of FIG. 6 in which a single resonant capacitance, shownin the uppermost primary cell and labeled C_(R), is used). Although fullbridge cells are shown in FIG. 4, the input cells may comprise any SACconfiguration (e.g., full bridge, half bridge, push-pull). Differenttypes of input cells may be combined in an adaptive array SAC. Forexample, a full-bridge input cell may be adaptively connected in serieswith a half-bridge input cell. Furthermore, power-sharing sub-arrays ofVTMs and/or SACs may be configured in adaptive arrays to provideincreased power capacity. The integrated adaptive array also may be usedin other converter topologies to provide an adjustable transformer turnsratio, which in the case of a VTM provides an adjustable voltagetransformation ratio. Accordingly, other embodiments are within thescope of the following claims.

1. A method of converting power from a source at an input voltage for delivery to a load, where the input voltage may vary between a high line voltage and a low line voltage, comprising: providing an integrated converter array having an input, an output, and a first input cell and a second input cell, each input cell having a respective number, Px, of turns and an output cell having a respective number, Sx, of turns; providing magnetic coupling between the turns to form a transformer common to the first and second input cells and the output cell; and configuring the input cells in a parallel connection for operation at the low line voltage and in a series connection for operation at the high line voltage.
 2. The method of claim 1 wherein: each input cell is driven by a voltage essentially equal to the input voltage in the parallel connection; and each input cell is driven by a voltage essentially equal to one-half of the input voltage in the series connection.
 3. The method of claim 1 wherein the integrated converter array comprises an integrated VTM array.
 4. The method of claim 3 further comprising providing, in the integrated VTM array, a method of converting power comprising: forming a resonant circuit including the transformer and having a characteristic resonant frequency and period; providing two or more primary switches in at least one of the input cells to drive the resonant circuit; and providing a switch controller to operate the primary switches in a series of converter operating cycles, each converter operating cycle characterized by two power transfer intervals of essentially equal duration, during which one or more of the primary switches are ON and power is transferred from the input of the integrated VTM array to the output of the integrated VTM array via the transformer, and voltages and currents in the integrated adaptive array rise and fall at the characteristic resonant frequency.
 5. The method of claim 3 further comprising: providing, in each of the first and second input cells, a positive-referenced switch and a negative-referenced switch connected to form a double-ended drive for the respective turns; connecting the respective turns of the first and second input cells to induce opposing flux in the transformer when driven by their respective positive-referenced switches; and providing a controller adapted to operate the switches of the first and second input cells substantially 180 degrees out of phase such that the positive-referenced switch of the first input cell and the negative-referenced switch of the second input cell are ON together and the negative-referenced switch of the first input cell and the positive-referenced switch of the second input cell are ON together.
 6. The method of claim 5 further comprising providing switches having a maximum voltage rating that is lower than the high line voltage.
 7. The method of claim 1 further comprising providing a circuit to sense the input voltage and to automatically configure the input cells in the series or parallel connections in response to the input voltage.
 8. The method of claim 1 wherein the integrated converter array comprises an integrated DC—DC converter array and regulation circuitry adapted to regulate an output of the integrated array.
 9. A method of converting power from an AC line at a line voltage for delivery to a load at a DC output voltage, where the line voltage may vary between a high line voltage and a low line voltage, comprising the method of claim 1 and further comprising: passing the AC line through a rectifier to produce a rectified line signal at a rectified voltage; using the integrated converter array for converting power received from the rectified line signal; providing rectification circuitry for delivering a unipolar output voltage; and wherein the rectified voltage is divided between the input cells when operating in series.
 10. The method of claim 9 further comprising providing capacitive energy storage between the unipolar output voltage and the load.
 11. The method of claim 9 wherein an input power is divided between the input cells when operating in parallel.
 12. The method of claim 10 further comprising providing regulation circuitry between the unipolar output voltage and the load.
 13. The method of claim 10 further comprising providing a power factor correction circuit between the unipolar output voltage and the capacitive energy storage.
 14. The method of claim 10 wherein the capacitive energy storage is provided at the output of the rectification circuitry.
 15. The method of claim 12 or 13 wherein the capacitive energy storage is provided at the load.
 16. The method of claim 11 further comprising providing a controller that senses the AC line voltage and configures the input cells in series when the AC line voltage is within an upper range and that configures the input cells in parallel when the AC line voltage is within a lower range.
 17. The method of claim 16 wherein said sensing comprises sensing the peak value of the rectified AC line voltage.
 18. The method of claim 17 further comprising comparing said peak value to a predetermined switchover threshold.
 19. The method of claim 17 wherein the upper range is between 226 V PEAK and 388 V PEAK.
 20. The method of claim 17 wherein the lower range is between 113 V PEAK and 195 V PEAK.
 21. The method of claim 18 wherein the switchover threshold is greater than voltages within the lower range.
 22. Apparatus for converting power from a source at an input voltage for delivery to a load, where the input voltage may vary between a high line voltage and a low line voltage, comprising: an integrated converter array having an input, an output, and a first input cell and a second input cell, each input cell having a respective number, Px, of turns and an output cell having a respective number, Sx, of turns; magnetic coupling between the turns to form a transformer common to the first and second input cells and the output cell; and configuration switches connected to configure the input cells in a parallel connection for operation at the low line voltage and in a series connection for operation at the high line voltage.
 23. The apparatus of claim 22 wherein: each input cell is driven by a voltage essentially equal to the input voltage in the parallel connection; and each input cell is driven by a voltage essentially equal to one-half of the input voltage in the series connection.
 24. The apparatus of claim 22 wherein the integrated converter array comprises an integrated VTM array.
 25. The apparatus of claim 24 further comprising: a resonant circuit including the transformer and having a characteristic resonant frequency and period; two or more primary switches in at least one of the input cells adapted to drive the resonant circuit; and a switch controller adapted to operate the primary switches in a series of converter operating cycles, each converter operating cycle characterized by two power transfer intervals of essentially equal duration, during which one or more of the primary switches are ON and power is transferred from the input of the integrated VTM array to the output of the integrated VTM array via the transformer, and voltages and currents in the integrated adaptive array rise and fall at the characteristic resonant frequency.
 26. The apparatus of claim 24 further comprising: wherein the first and second input cells comprise a positive-referenced switch and a negative-referenced switch connected to form a double-ended drive for the respective turns; the respective turns of the first and second input cells being connected to induce opposing flux in the transformer when driven by their respective positive-referenced switches; and a controller adapted to operate the switches of the first and second input cells substantially 180 degrees out of phase such that the positive-referenced switch of the first input cell and the negative-referenced switch of the second input cell are ON together and the negative-referenced switch of the first input cell and the positive-referenced switch of the second input cell are ON together.
 27. The apparatus of claim 26 wherein the switches comprise a maximum voltage rating that is lower than the high line voltage.
 28. The apparatus of claim 22 further comprising a circuit adapted to sense the input voltage and to automatically configure the input cells in the series or parallel connections in response to the input voltage.
 29. The apparatus of claim 22 wherein the integrated converter array comprises an integrated DC—DC converter array and regulation circuitry adapted to regulate an output of the integrated array.
 30. Apparatus for converting power from an AC line at a line voltage for delivery to a load at a DC output voltage, where the line voltage may vary between a high line voltage and a low line voltage, comprising the apparatus of claim 22 and further comprising: a rectifier having an input connected to the AC line to produce a rectified line signal at a rectified voltage; the integrated converter array being adapted to convert power received from the rectified line signal; wherein the output cell includes rectification circuitry for delivering a unipolar output voltage; and wherein the rectified voltage is divided between the input cells in the series connection.
 31. The apparatus of claim 30 further comprising capacitive energy storage connected between the unipolar output voltage and the load.
 32. The apparatus of claim 30 wherein an input power is divided between the input cells in the parallel connection.
 33. The apparatus of claim 31 further comprising regulation circuitry having an input connected to receive power from the unipolar output voltage and an output for delivering power to the load.
 34. The apparatus of claim 31 further comprising a power factor correction circuit having an input connected to receive power from the unipolar output voltage and an output for delivering power to the capacitive energy storage.
 35. The apparatus of claim 31 wherein the capacitive energy storage is connected across the output of the rectification circuitry.
 36. The apparatus of claim 33 or 34 wherein the capacitive energy storage is connected across the load.
 37. The apparatus of claim 32 further comprising a controller adapted to sense the AC line voltage and to configure the input cells in the series connection when the AC line voltage is within an upper range and to configure the input cells in the parallel connection when the AC line voltage is within a lower range.
 38. The apparatus of claim 37 wherein the controller is adapted to sense the peak value of the rectified AC line voltage.
 39. The apparatus of claim 38 wherein the controller is adapted to compare said peak value to a predetermined switchover threshold.
 40. The apparatus of claim 38 wherein the upper range is between 226 V PEAK and 388 V PEAK.
 41. The apparatus of claim 38 wherein the lower range is between 113 V PEAK and 195 V PEAK.
 42. The apparatus of claim 39 wherein the switchover threshold is greater than voltages within the lower range.
 43. The apparatus of claim 23 wherein each input cell comprises a voltage transformation ratio, K=4. 